The base oils for hydrocarbon lubricating oils are generally produced in refineries from distillates. These base oil streams are often produced in several steps, in plants that may use solvent extraction, solvent dewaxing, and hydrogen treatment. To be able to meet the demands of modem engines, particularly those of internal combustion engines, various additives are often incorporated in the base oil. Such additives include, for example, antioxidants, pour point depressants, viscosity index improvers, detergents, dispersants, and other additives.
In use lubricating oils are generally not consumed in the usual sense and, except for some loss, are recovered as used oils. In the case of motor oils, usually more than 60% of the original oil is recovered when the oil is changed. Oil changes are necessary because in use the oil is contaminated with unburned fuel, metal particles, carbon particles, tars, polymerized material and the like. Used oil also becomes contaminated, inter alia, by combustion products which are kept dispersed by the added dispersants. Used oil also on analysis has a high ash content, typically in the range of 1%-2% by weight of the oil, due to metals (mainly Ca, Ba, and Zn) which were added to the base oil as ingredients of additives.
Used lubricating oil also usually contains significant amounts of moisture. The water content of freshly dined used lubricating oil is usually less than 0.5%. However, the water content increases dramatically during collection as a rest of condensation, contamination, or both, for example. Typically, waste crankcase oil at collection centers contains about 7% water by volume.
More than one billion gallons of lubricating oil are used in the United States on a yearly basis, according to the National Oil Recycles Association. Substantial quantities of this oil are available for disposal, somehow, after use. Collection centers for used oil are available in most cities, to encourage the use of environmentally acceptable or beneficial disposal techniques. Even so, of all the used oil that is potentially available for recovery, about 25% is unaccounted for.
Only about 75% of the used oil generated in the United States is currently being reclaimed each year. Ideally, all of the used oil should be reclaimed in order to avoid the damage to the environment that is caused by improper disposal.
However, even reclaimed oil causes environmental concern because of its high content of ash forming materials. Reclaimed oil is now primarily used as a fuel by being blended with virgin fuel to meet stack emission standards. Based on an analyzed ash content of 1% by weight of the oil, each million gallons of reclaimed oil that is burned releases about 37 tons of ash into the air. Since there may be 800 million gallons or so of used oil per year, curtly, in the United States, use of the used oil as a fuel is not an attractive approach from an environmental standpoint.
After the ash-forming materials are removed by the present invention such oils become useful as non-polluting heating fuel, marine fuel diesel fuel, and petroleum refinery cracker feed. In the past, recovered used lube oil has not been useful to oil refineries.
So far as is known, the prior art does not teach a heat-treating-filtration process for wet used oil that yields a product that has an ash content as low as 0.01%, 0.001%, or even lower but such levels can be achieved by preferred embodiments of the process of the present invention.